“But some part of him realized, even as he fought to break free from Lupin, that Sirius had never kept him waiting before. . . . Sirius had risked everything, always, to see Harry, to help him. . . . If Sirius was not reappearing out of that archway when Harry was yelling for him as though his life depended on it, the only possible explanation was that he could not come back. . . . That he really was . . .”